An X-ray film system including a fluorescent screen provided with an X-ray phosphor layer therein and a double-faced coating material has been generally used for X-ray radiographing until now. A recent digital radiation detection apparatus with an X-ray phosphor layer and two-dimensional photodetectors has the following advantages and has been vigorously researched and developed. Applications for various patents thereon have been filed. That is to say, the digital radiation detection apparatus is superior in image characteristic and can share data with networked computers because it handles digital data.
Among other digital radiation detection apparatus, an apparatus disclosed in Japanese Patent Application Laid-Open No. 2000-284053 (patent family: U.S. Pat. No. 6,262,422, EP0903590 A1, and CN1501095(A)) is known as a highly sensitive and sharp apparatus. The apparatus forms a scintillator layer for converting radiation into light detectable on photodetectors. The photodetectors consist of a plurality of photosensors and photoelectric conversion units in which electric elements such as thin film transistors (TFT) serving as switching elements are two-dimensionally arranged.
Over a light receiving unit is formed a columnar crystal structured scintillator which is a wavelength converter for converting incident radiation into visible light and which consists of a columnar crystallized phosphor layer of alkali halide. A protective film is formed over the scintillator.
Incidentally, there are still the following problems to be solved in the photoelectric conversion unit: decreasing characteristic variation due to aging and S/N ratio reduction due to dark current, and shortening a photographing cycle to make the apparatus easy to use.
Emitting light before radiographing to decrease dark current permits one to provide an X-ray image high in S/N ratio in a short time. Thus, the emission of light to the photoelectric conversion unit by a light source is called “light reset,” “bias light application” or “light calibration.”
On the other hand, a conventional radiation detection apparatus disclosed in Japanese Patent Application Laid-Open No. 2004-33659 directly converts radiation into electric charge and is provided with a light source for applying light to an X-ray flat panel detector to suppress reduction in sensitivity of the detector.
However, the radiation detection apparatus including a wavelength converter to which the above light source is added is thickened, and thus is increased in size.
Furthermore, the addition of the composing element of the light source increases cost.